1997 Chevy Van Doors locking continuously but not when pass

Our van is continuously locking its doors. I took the batteries out of the keyfob and it still does it. Then, while poking around for a stuck lock/unlock switch I noticed that the car does not lock itself when the rear passenger side is open. If I push the sensor that determines if the door is shut with my finger, it starts again. That particular door does not have a switch on it, only a manual release.